Civil Engineer Society

How to Fix : AutoCAD | The security system (Softlock license manager) is not functioning or is improperly installed

2019-08-30T18:03:00.000+08:00

How to Fix : AutoCAD | The security system (Softlock license manager) is not functioning or is improperly installed for Windows

This error can happen if you have a corrupted installation of an Autodesk program or if the License model has been changed in the registry. In most cases a clean uninstall and reinstall should correct the issue. However if this issue is not resolved then delete the licensing files and reactivate the product.

License files location ;

For Windows 10 / Windows 8 / Windows 7 / Windows Vista ;

C:\ProgramData\FLEXnet\adskflex_00691b00_tsf.data

C:\ProgramData\FLEXnet\adskflex_00691b00_tsf.data.backup

For Windows XP ;

C:\Documents and Settings\All Users\Application Data\FLEXnet\adskflex_00691b00_tsf.data

C:\Documents and Settings\All Users\Application Data\FLEXnet\adskflex_00691b00_tsf.data.backup

CSI SAFE : How To Check Slab Deflection

2017-02-24T22:39:00.002+08:00

CSI SAFE : How To Check Slab Deflection

SAFE can use user-defined reinforcement to compute cracked-slab deflection. For this option, select Run > Reinforcing Option for Cracking Analysis, then select User Specified Rebars in Reinforcement Source. Select Draw Slab Rebar from the vertical menu on the left. Note that rebar must be added in both the tension and compression regions for the entire slab since the software will only use the user-defined reinforcement, and not use the reinforcement design.

Cracked-section analysis is run in SAFE using either of the following two methods ;

1) All load patterns are applied in a single load case which uses either immediate or long-term cracked deflection

2) A single load pattern is applied in a load case, then another case is set to continue From State at End of Nonlinear Case.

In SAFE, Two types of cracked-section analysis are available, including ;

1) Immediate cracked deflection

2) Long-term cracked deflection accounting for creep and shrinkage

Long-term cracked deflection, in which analysis is divided into the following two categories:

1) Non-sustained portion, in which cracked-section analysis considers only the non-sustained portion of LIVE load, solving for incremental deflection.

b) Sustained portion, in which long-term cracked analysis considers the sustained loading from DEAD, SDEAD, and a portion of the LIVE load. Creep and shrinkage are included only in this sustained portion of analysis because these effects are only applicable under sustained loading.

Most engineers simply check this values against ACI 318 Table 9.5(b), since this will always result in safe and conservative design.

Concrete Curing Techniques

2017-02-22T23:28:00.001+08:00

Concrete Curing Techniques

Overview of concrete curing technique

During the curing period, concrete is ideally maintained at controlled temperature and humidity. To ensure full hydration during curing, concrete slabs are often sprayed with "curing compounds" that create a water-retaining film over the concrete. Typical films are made of wax or related hydrophobic compounds. After the concrete is sufficiently cured, the film is allowed to abrade from the concrete through normal use.

Traditional conditions for curing involve by spraying or ponding the concrete surface with water. The picture to the right shows one of many ways to achieve this, ponding – submerging setting concrete in water and wrapping in plastic to prevent dehydration. Additional common curing methods include wet burlap and/or plastic sheeting covering the fresh concrete.

For higher-strength applications, accelerated curing techniques may be applied to the concrete. One common technique involves heating the poured concrete with steam, which serves to both keep it damp and raise the temperature, so that the hydration process proceeds more quickly and more thoroughly.

Techniques 1 : Shading

The object of shading concrete work is to prevent the evaporation of water from the surface even before setting. This is adopted mainly in case of large concrete surfaces such as road slabs. This is essential in dry weather to protect the concrete from heat, direct sun rays and wind. It also protects the surface from rain. In cold weather shading helps in preserving the heat of hydration of cement thereby preventing freezing of concrete under mild frost conditions. Shading may be achieved by using canvas stretched on frames. This method has a limited application only.

Techniques 2 : Cover

This is a widely used method of curing, particularly for structural concrete. Thus exposed surface of concrete is prevented from drying out by covering it with hessian, canvas or empty cement bags. The covering over vertical and sloping surfaces should be secured properly. These are periodically wetted. The interval of wetting will depend upon the rate of evaporation of water. It should be ensured that the surface of concrete is not allowed to dry even for a short time during the curing period. Special arrangements for keeping the surface wet must be made at nights and on holidays.

Techniques 3 : Water Sprinkling

Sprinkling of water continuously on the concrete surface provides an efficient curing. It is mostly used for curing floor slabs. The concrete should be allowed to set sufficiently before sprinkling is started. The spray can be obtained from a perforated plastic box. On small jobs sprinkling of water may be done by hand. Vertical and sloping surfaces can be kept continuously wet by sprinkling water on top surfaces and allowing it to run down between the forms and the concrete. For this method of curing the water requirement is higher.

Techniques 4 : Water Ponding

This is the best method of curing. It is suitable for curing horizontal surfaces such as floors, roof slabs, road and air field pavements. The horizontal top surfaces of beams can also be ponded. After placing the concrete, its exposed surface is first covered with moist hessian or canvas. After 24 hours, these covers are removed and small ponds of clay or sand are built across and along the pavements. The area is thus divided into a number of rectangles.

The water is filled between the ponds. The filling of water in these ponds is done twice or thrice a day, depending upon the atmospheric conditions. Though this method is very efficient, the water requirement is very heavy. Ponds easily break and water flows out. After curing it is difficult to clean the clay.

Techniques 5 : Membrane curing

The method of curing described above come under the category of moist curing. Another method of curing is to cover the wetted concrete surface by a layer of water proof material, which is kept in contact with the concrete surface of seven days. This method of curing is termed as membrane curing. A membrane will prevent the evaporation of water from the concrete. The membrane can be either in solid or liquid form. They are also known as sealing compounds. Bituminised water proof papers, wax emulsions, bitumen emulsions and plastic films are the common types of membrane used.

Whenever bitumen is applied over the surface for curing, it should be done only after 24 hours curing with gunny bags. The surface is allowed to dry out so that loose water is not visible and then the liquid asphalt sprayed throughout. The moisture in the concrete is thus preserved. It is quite enough for curing.

This method of curing does not need constant supervision. It is adopted with advantage at places where water is not available in sufficient quantity for wet curing. This method of curing is not efficient as compared with wet curing because rate of hydration is less. Moreover the strength of concrete cured by any membrane is less than the concrete which is moist cured. When membrane is damaged the curing is badly affected.

Techniques 6 : Steam curing

Steam curing and hot water curing is sometimes adopted. With these methods of curing, the strength development of concrete is very rapid. These methods can best be used in pre cast concrete work. In steam curing the temperature of steam should be restricted to a maximum of 750C as in the absence of proper humidity (about 90%) the concrete may dry too soon. In case of hot water curing, temperature may be raised to any limit, ay 1000C.

At this temperature, the development of strength is about 70% of 28 days strength after 4 to 5 hours. In both cases, the temperature should be fully controlled to avoid non-uniformity. The concrete should be prevented from rapid drying and cooling which would form cracks.

Function of Concrete Curing

2017-02-20T22:34:00.002+08:00

Function of Concrete Curing

Concrete Curing plays an important role on strength development and durability of concrete. Curing takes place immediately after concrete placing and finishing, and involves maintenance of desired moisture and temperature conditions, both at depth and near the surface, for extended periods of time. Curing is the hydration process that occurs after the concrete has been placed

Definition of Concrete Curing
Curing of concrete is defined as providing adequate moisture, temperature, and time to allow the concrete to achieve the desired properties for its intended use. Curing of concrete is done to maintain the Optimum moisture content (OMC) i.e. to prevent the loss of water which is required for the hydration of cement, to avoid shrinkage cracks and premature stressing or disturbance in concrete.

Hydration and hardening of concrete
Hydration and hardening of concrete during the first three days is critical. Abnormally fast drying and shrinkage due to factors such as evaporation from wind during placement may lead to increased tensile stresses at a time when it has not yet gained sufficient strength, resulting in greater shrinkage cracking. The early strength of the concrete can be increased if it is kept damp during the curing process. Minimizing stress prior to curing minimizes cracking.

Increase early and ultimate compression strength
High-early-strength concrete is designed to hydrate faster, often by increased use of cement that increases shrinkage and cracking. The strength of concrete changes (increases) for up to three years. It depends on cross-section dimension of elements and conditions of structure exploitation. Addition of short-cut polymer fibers can improve (reduce) shrinkage-induced stresses during curing and increase early and ultimate compression strength.

Increased strength and lower permeability and avoids cracking
Properly curing concrete leads to increased strength and lower permeability and avoids cracking where the surface dries out prematurely. Care must also be taken to avoid freezing or overheating due to the exothermic setting of cement. Improper curing can cause scaling, reduced strength, poor abrasion resistance and cracking.

Construction of The Brooklyn Bridge

2017-02-19T12:40:00.000+08:00

Construction of The Brooklyn Bridge

The Brooklyn Bridge is one of the oldest suspension bridges in the United States and the first constructed using steel wire. Completed in 1883, The Brooklyn Bridge took just over 13 years (1870-83) from start of construction until opening, or 18 years (1865-83), from the drawing-board to opening. Actual construction took 13 years, starting on January 3rd 1870 and the bridge opened for public use on May 24, 1883.

Introducing the Brooklyn Bridge

The Brooklyn Bridge has been sometimes called the Eighth Wonder of the World and was recognized as possibly the greatest feat of Brooklyn Bridge-engineering during the nineteenth century. This was contributed to by the fact that whilst many bridges were constructed in that century, conversely many collapsed. This generally occurred either within a few decades or sometimes within a few years.

A decision was taken for the building of the Brooklyn Bridge, primarily for the provision of faster and convenient commuting between Brooklyn and Manhattan, the financial center of New York City. The journey by automobile and the ferry service operating at that time, was both costly and time consuming.

The Initial Design of John Roebling - And Some Problems

Brooklyn Bridge ConsturctionIt was in 1869 that the New York Bridge Company was formed by John Roebling and his design for the bridge accepted. However, discussions concerning the construction of the bridge and the financial, technical and political aspects, took place over a period of about sixty years. During the early stages of construction, John Roebling was involved in an accident, the result of which caused his death. Washington Roebling his son replaced him as chief engineer and remained in various capacities with the project until bridge construction was completed.

The Structure and the Caissons

Caissons were an integral part of the construction for the towers in the building of the Brooklyn Bridge. They had the appearance of large, wooden boxes open at the bottom. After being towed into position, they were then sunk to the river bed; workers were placed inside, for the purpose of digging mud and debris from the river bed. To prevent the caissons flooding, compressed air was pumped in.

The stone towers were constructed on top of the caissons and as the work progressed, the workers inside, named “sand hogs” dug deeper. Upon reaching bedrock, the digging ceased and the caissons were then filled with concrete. The foundations for the bridge were thus formed. Today, the Brooklyn caisson lies forty four feet beneath the surface of the water. It was necessary to settle the Manhattan caisson deeper and this lies seventy eight feet beneath the surface.

Some Notable Facts

The Brooklyn Bridge is the longest suspension bridge of its era and when built, was the highest free standing structure of the Northern hemisphere. With a span of over six thousand feet, on ramps included, the bridge incorporates ropes made from steel, which were manufactured six times stronger than required for supports.

Workers lives were lost during the building of the Brooklyn Bridge. Whilst no official records were maintained, a booklet compiled by the Master Mechanic named Farrington and supported by Chief Engineer William Kingsley, stated that twenty men died. This again is supported by newspaper reports and on occasions in minutes of the Bridge Company meetings.

A bridge of “Firsts:” The Brooklyn Bridge was the original suspension bridge to utilize steel for the cable wire and the usage of pneumatic caissons. Another dangerous first is the use of explosives within the confines of a caisson. It is also recorded that at the time of completion, this 3460 feet in length suspension bridge was the longest of its kind in the world, being fifty percent longer than any other suspension bridge!

A bridge of “Height:” The towers loom 276½ feet above the water at high tide. As a comparison in 1883, the spire of Trinity church was Brooklyn Bridge Walk281 feet. From the roadway, the towers reach a height of 159 feet and the tower arches 117 feet. The height of the roadbed from the water is 135 feet.

Bridge Calamities: during the building of the Brooklyn Bridge those included the death of John A. Roebling and the illness and disablement of his son, Washington. Other occurrences that took place were a caisson fire, an explosion, and the discovery of fraud on the part of a contractor. The Brooklyn Bridge opened - May 24, 1883, 2:00 pm. On that day, the Irish workers demonstrated with a protest against “Opening Day” coinciding with the birthday of Queen Victoria of England.

Workability of Concrete

2017-02-17T23:49:00.003+08:00

Workability of Concrete

What is the definition of workability? 'workability' is the ability of a fresh (plastic) concrete mix to fill the form/mold properly with the desired work (vibration) and without reducing the concrete's quality. Workability of concrete depends on water content, aggregate (shape and size distribution), cementitious content and age (level of hydration) and can be modified by adding chemical admixtures, like superplasticizer.

Raising the water content or adding chemical admixtures increases concrete workability. Excessive water leads to increased bleeding and/or segregation of aggregates (when the cement and aggregates start to separate), with the resulting concrete having reduced quality. The use of an aggregate blend with an undesirable gradation can result in a very harsh mix design with a very low slump, which cannot readily be made more workable by addition of reasonable amounts of water.

An undesirable gradation can mean using a large aggregate that is too large for the size of the formwork, or which has too few smaller aggregate grades to serve to fill the gaps between the larger grades, or using too little or too much sand for the same reason, or using too little water, or too much cement, or even using jagged crushed stone instead of smoother round aggregate such as pebbles. Any combination of these factors and others may result in a mix which is too harsh, ie, which does not flow or spread out smoothly, is difficult to get into the formwork, and which is difficult to surface finish.

How to determine workability of concrete ?

Workability can be measured by the concrete slump test, a simple measure of the plasticity of a fresh batch of concrete following the ASTM C 143 or EN 12350-2 test standards. Slump is normally measured by filling an "Abrams cone" with a sample from a fresh batch of concrete. The cone is placed with the wide end down onto a level, non-absorptive surface. It is then filled in three layers of equal volume, with each layer being tamped with a steel rod to consolidate the layer.

When the cone is carefully lifted off, the enclosed material slumps a certain amount, owing to gravity. A relatively dry sample slumps very little, having a slump value of one or two inches (25 or 50 mm) out of one foot (305 mm). A relatively wet concrete sample may slump as much as eight inches. Workability can also be measured by the flow table test.

Slump can be increased by addition of chemical admixtures such as plasticizer or superplasticizer without changing the water-cement ratio. Some other admixtures, especially air-entraining admixture, can increase the slump of a mix. High-flow concrete, like self-consolidating concrete, is tested by other flow-measuring methods. One of these methods includes placing the cone on the narrow end and observing how the mix flows through the cone while it is gradually lifted. After mixing, concrete is a fluid and can be pumped to the location where needed.

What is the factors which affect workability of concrete

Cement content of concrete
Water content of concrete
Mix proportions of concrete
Size of aggregates
Shape of aggregates
Grading of aggregates
Surface texture of aggregates
Use of admixtures in concrete
Use of supplementary cementitious materials

Slump Test for Concrete | Procedure and Interpretation of Results

2017-02-16T22:18:00.001+08:00

Slump Test for Concrete | Procedure and Interpretation of Results

The concrete slump test measures the consistency of fresh concrete before it sets. It is performed to check the workability of freshly made concrete, and therefore the ease with which concrete flows. It can also be used as an indicator of an improperly mixed batch. The test is popular due to the simplicity of apparatus used and simple procedure. The slump test is used to ensure uniformity for different loads of concrete under field conditions.

Procedure for Slump Test for Concrete

The test is carried out using a metal mould in the shape of a conical frustum known as a slump cone or Abrams cone, that is open at both ends and has attached handles.

The tool typically has an internal diameter of 100 millimetres (3.9 in) at the top and of 200 millimetres (7.9 in) at the bottom with a height of 305 millimetres (12.0 in).

The cone is placed on a hard non-absorbent surface. This cone is filled with fresh concrete in three stages.

Each time, each layer is tamped 25 times with a 2 ft (600 mm)-long bullet-nosed metal rod measuring (16 mm) in diameter.

At the end of the third stage, the concrete is struck off flush with the top of the mould. The mould is carefully lifted vertically upwards, so as not to disturb the concrete cone.

The concrete then slumps (subsides). The slump of the concrete is measured by measuring the distance from the top of the slumped concrete to the level of the top of the slump cone.

Result of Slump Test

The slumped concrete takes various shapes, and according to the profile of slumped concrete, the slump is termed as true slump, shear slump or collapse slump. If a shear or collapse slump is achieved, a fresh sample should be taken and the test repeated. A collapse slump is an indication that the mix is too wet.

Only a true slump is of any use in the test. A collapse slump will generally mean that the mix is too wet or that it is a high workability mix, for which the slump test is not appropriate. Very dry mixes having slump 0 – 25 mm are typically used in road making, low workability mixes having slump 10 – 40 mm are typically used for foundations with light reinforcement.

Medium workability mixes with slump 50 – 90 mm, are typically used for normal reinforced concrete placed with vibration, high workability concrete with slump higher than 100 mm is typically used where reinforcing has tight spacing, and/or the concrete has to flow a great distance.

Limitations of the Slump Test

The slump test is suitable for slumps of medium to high workabiity, slump in the range of 5 – 260 mm, the test fails to determine the difference in workability in stiff mixes which have zero slump, or for wet mixes that give a collapse slump. It is limited to concrete formed of aggregates of less than 38 mm (1.5 inch).

Composition of Concrete

2017-02-15T23:20:00.001+08:00

Composition of Concrete

Compostion of concrete is made up of three main ingredients ehich is water, cement, and aggregates. The ratio of the ingredients changes the properties of the final product, which allows the engineer to design concrete that meets their specific needs. Admixtures are added to adjust the concrete mixture for specific performance criteria. The mix design depends on the type of structure being built, how the concrete is mixed and delivered, and how it is placed to form the structure. The main composition that can be found in concrete are as below ;

Aggregate
Aggregate consists of large chunks of material in a concrete mix, generally a coarse gravel or crushed rocks such as limestone, or granite, along with finer materials such as sand.

Cement
Cement, most commonly Portland cement, is associated with the general term "concrete." A range of materials can be used as the cement in concrete. One of the most familiar of these alternative cements is asphalt concrete. Other cementitious materials such as fly ash and slag cement, are sometimes added as mineral admixtures (see below) - either pre-blended with the cement or directly as a concrete component - and become a part of the binder for the aggregate.

To produce concrete from most cements (excluding asphalt), water is mixed with the dry powder and aggregate, which produces a semi-liquid that workers can shape, typically by pouring it into a form. The concrete solidifies and hardens through a chemical process called hydration. The water reacts with the cement, which bonds the other components together, creating a robust stone-like material.

Reinforcement bar
Reinforcement is often included in concrete. Concrete can be formulated with high compressive strength, but always has lower tensile strength. For this reason it is usually reinforced with materials that are strong in tension, often steel.

Chemical admixtures
Chemical admixtures are added to achieve varied properties. These ingredients may accelerate or slow down the rate at which the concrete hardens, and impart many other useful properties including increased tensile strength, entrainment of air, and/or water resistance.

Mineral admixtures
Mineral admixtures are becoming more popular in recent decades. The use of recycled materials as concrete ingredients has been gaining popularity because of increasingly stringent environmental legislation, and the discovery that such materials often have complementary and valuable properties. The most conspicuous of these are fly ash, a by-product of coal-fired power plants, ground granulated blast furnace slag, a byproduct of steelmaking, and silica fume, a byproduct of industrial electric arc furnaces.

The use of these materials in concrete reduces the amount of resources required, as the mineral admixtures act as a partial cement replacement. This displaces some cement production, an energetically expensive and environmentally problematic process, while reducing the amount of industrial waste that must be disposed of. Mineral admixtures can be pre-blended with the cement during its production for sale and use as a blended cement, or mixed directly with other components when the concrete is produced.

Mariana Trench : The Deepest Part of the World's Oceans

2017-02-14T21:59:00.002+08:00

Mariana Trench : The Deepest Part of the World's Oceans

The Mariana Trench maximum-known depth about 10,994 metres

The Mariana Trench located in the western Pacific Ocean, to the east of the Mariana Islands. The trench is about 2,550 kilometres long with an average width of 69 kilometres . The Mariana Trench maximum-known depth about 10,994 metres (36,070 ft) at a small slot-shaped valley in its floor known as the 'Challenger Deep', at its southern end, although some unrepeated measurements place the deepest portion at 11,034 metres (36,201 ft).

Pressure at the bottom of Mariana Trench can reach up to 108 MegaPascal !

At the bottom of the trench the water column above exerts a pressure of 108 MegaPascal (1,086 bars /15,750 psi), more than 1,000 times the standard atmospheric pressure at sea level. At this pressure, the density of water is increased by 4.96%, so that 95 litres of water under the pressure of the Challenger Deep would contain the same mass as 100 litres at the surface. The temperature at the bottom is 1 to 4 °C (34 to 39 °F).

The temperature at the bottom of Mariana Trench is about 1 to 4 °C (34 to 39 °F).

The trench is not the part of the seafloor closest to the center of the Earth. This is because the Earth is not a perfect sphere; its radius is about 25 kilometres (16 mi) less at the poles than at the equator. As a result, parts of the Arctic Ocean seabed are at least 13 kilometres (8.1 mi) closer to the Earth's center than the Challenger Deep seafloor.

The Challenger Deep is the deepest known point in the Earth's seabed hydrosphere

With a depth of 10,898 to 10,916 m (35,755 to 35,814 ft) by direct measurement from submersibles, and slightly more by sonar bathymetry. The closest land to the Challenger Deep is Fais Island (one of the outer islands of Yap), 287 km (178 mi) southwest, and Guam, 304 km (189 mi) to the northeast. It is located in the ocean territory of the Federated States of Micronesia, 1.6 km (1 mi) from its border with ocean territory associated with Guam.

Chemical Admixtures in Concrete Mix : Plasticizers

2017-02-14T21:31:00.000+08:00

Chemical Admixtures in Concrete Mix : Plasticizers

Plasticizers or water reducers, and superplasticizer or high range water reducers, are chemical admixtures that can be added to concrete mixtures to improve workability. Unless the mix is "starved" of water, the strength of concrete is inversely proportional to the amount of water added or water-cement (w/c) ratio. In order to produce stronger concrete, less water is added, which makes the concrete mixture less workable and difficult to mix, necessitating the use of plasticizers, water reducers, superplasticizers or dispersants.

1. To achieve a higher strength by decreasing the water cement ratio at the same workability as an admixture free mix.

2. To achieve the same workability by decreasing the cement content so as to reduce the heat of hydration in mass concrete.

3. To increase the workability so as to ease placing in accessible locations

4. Water reduction more than 5% but less than 12%

5. The commonly used admixtures are Ligno-sulphonates and hydrocarbolic acid salts.

6. Plasticizers are usually based on lignosulphonate, which is a natural polymer, derived from wood processing in the paper industry.

Actions involved ;

Dispersion

Surface active agents alter the physic chemical forces at the interface. They are adsorbed on the cement particles, giving them a negative charge which leads to repulsion between the particles. Electrostatic forces are developed causing disintegration and the free water become available for workability.

Lubrication

As these agents are organic by nature, thus they lubricate the mix reducing the friction and increasing the workability.

Retardation

A thin layer is formed over the cement particles protecting them from hydration and increasing the setting time. Most normal plasticizers give some retardation, 30–90 minutes.

Chemical Admixtures in Concrete Mix

2017-02-13T22:56:00.002+08:00

Chemical Admixtures in Concrete Mix

Chemical admixtures are materials in the form of powder or fluids that are added to the concrete to give it certain characteristics not obtainable with plain concrete mixes. In normal use, admixture dosages are less than 5% by mass of cement and are added to the concrete at the time of batching/mixing. The common types of admixtures which will be discussed as follows ; accelerators, retarders , air entraining agents, plasticizers, pigments, corrosion inhibitors, bonding agents, and pumping aids

Accelerators
Accelerators speed up the hydration (hardening) of the concrete. Typical materials used are CaCl
2, Ca(NO3)2 and NaNO3. However, use of chlorides may cause corrosion in steel reinforcing and is prohibited in some countries, so that nitrates may be favored. Accelerating admixtures are especially useful for modifying the properties of concrete in cold weather.

Retarders
Retarders slow the hydration of concrete and are used in large or difficult pours where partial setting before the pour is complete is undesirable. Typical polyol retarders are sugar, sucrose, sodium gluconate, glucose, citric acid, and tartaric acid.

Air entraining agents
Air entraining agents add and entrain tiny air bubbles in the concrete, which reduces damage during freeze-thaw cycles, increasing durability. However, entrained air entails a trade off with strength, as each 1% of air may decrease compressive strength 5%.[33] If too much air becomes trapped in the concrete as a result of the mixing process, Defoamers can be used to encourage the air bubble to agglomerate, rise to the surface of the wet concrete and then disperse.

Plasticizers
Plasticizers increase the workability of plastic or "fresh" concrete, allowing it be placed more easily, with less consolidating effort. A typical plasticizer is lignosulfonate. Plasticizers can be used to reduce the water content of a concrete while maintaining workability and are sometimes called water-reducers due to this use. Such treatment improves its strength and durability characteristics. Superplasticizers (also called high-range water-reducers) are a class of plasticizers that have fewer deleterious effects and can be used to increase workability more than is practical with traditional plasticizers. Compounds used as superplasticizers include sulfonated naphthalene formaldehyde condensate, sulfonated melamine formaldehyde condensate, acetone formaldehyde condensate and polycarboxylate ethers.

Pigments
Pigments can be used to change the color of concrete, for aesthetics.

Corrosion inhibitors
Corrosion inhibitors are used to minimize the corrosion of steel and steel bars in concrete.

Bonding agents
Bonding agents are used to create a bond between old and new concrete (typically a type of polymer) with wide temperature tolerance and corrosion resistance.

Pumping aids
Pumping aids improve pumpability, thicken the paste and reduce separation and bleeding.

Types of Concrete Batching Plant

2017-02-12T22:27:00.001+08:00

Types of Concrete Batching Plant

Concrete batching plant also known as a batch plant or batching plant or a concrete batching plant, is equipment that combines various ingredients to form concrete. Some of these inputs include water, air, admixtures, sand, aggregate (rocks, gravel, etc.), fly ash, silica fume, slag, and cement. There are several types of concrete batching plant which is very common in construction industries which is ready mix plant, central mix plant and temporary batch plant.

Ready Mix Plant
A ready mix concrete plant weighs the sand, gravel and cement in weigh batchers which can be computer assisted. All the ingredients then combine in a confining chute which discharges into the ready mix truck. Meanwhile, water is either being weighed or volumetrically metered and discharged through the same confining chute into the ready mix truck. These ingredients are then mixed for a minimum of 10 minutes during transportation to the job site. There is also lots of benefit for choosing ready mix concrete compared to others mix.

Central Mix or Products Plant
A central mix or products plant combines some or all of the above ingredients (including water) at a central location in a mixer. The final product is then transported to the desired location. Central mix or products plants differ from ready mix plants in that they contain a central mixer, which can offer a more consistent mixture in a shorter time (generally 5 minutes or less).

Temporary Batch Plant
A temporary batch plant can be constructed on a large job site. A ready mix concrete plant becomes central mix with the addition of a concrete mixer.

Benefits of Using Ready-Mixed Concrete

2017-02-11T16:48:00.004+08:00

The Pros And Cons Of Using Ready-Mixed Concrete

Learning about the benefit of using ready mix concrete whill help you to consider each option will help you make decision as to which is ideal for your situation. Here are some of the benefits of using a ready-mixed concrete for your home construction project.

Benefits of Using Ready-Mixed Concrete

Ready-Mixed Concrete is a Stronger Grade of Concrete

One of the biggest advantages to use a ready-mixed concrete is that most ready-mixed concretes are a stronger grade of concrete compared to those you mix yourself. There are many different types and grades of concrete based on the water-to-sediment ratio and the types of sediment and aggregate used. However, a concrete mixing truck can mix stronger sediment than small concrete mixers that are used to mix on-site concrete mixes. As such, you can get a stronger grade of concrete, which ultimately has a longer lifespan and is more durable, if you go with a ready-mixed concrete.

Ready-Mixed Concrete Will Cure Faster

The other advantage to a ready-mixed concrete is that it will cure faster. As was discussed in the disadvantages section, ready-mixed concrete is mixing while it is being transported. This can be a negative thing if you aren’t quick to lay out and smooth your concrete. But if you know what you are doing and are prepared, having concrete that cures fast can also be beneficial. If the weather is not ideal for concrete laying, such as when it is cold or rainy, you will want your concrete to harden quickly. If there are concerns that children or animals may walk through the concrete, you will want it to harden quickly. Therefore, concrete that is already mixing and ready to enter the curing stage in a brief amount of time can be beneficial in those circumstances.

Disadvantages of Using Ready-Mixed Concrete

You Have to Work Fast When Using Ready-Mixed Concrete

One of the biggest downsides to using a ready-mixed concrete is that you have to work fast when laying this type of concrete. This type of concrete begins mixing when it is loaded into the concrete mixing truck. It continues mixing while it is en-route to your home on construction site for delivery. There are many factors that affect how long it takes for concrete to begin to cure, or harden, including the sediment to water ratio of the mix and weather conditions. However, since ready-mixed concrete is mixing while it is being transported, you have less time to spread it before it begins to cure compared with concretes that you mix on-site. As such, you need to either be quick to spread, level and smooth ready-mixed concrete or have helpers on hand. Otherwise, this type of concrete can harden before you can complete your project.

You Have to Have an Accessible Area for the Concrete Mixing Truck

The other disadvantage to ready-mixed concrete is that your concrete is delivered in a large, concrete mixing truck. In order for this truck to deliver the concrete, you need an accessible area for it. If you live in a residential neighborhood, with small streets, this can be challenging. Before you decide to go this route, make sure there is enough space for a truck of this size to get to your construction site.

Earthquake Effect Around the World

2017-02-09T22:38:00.000+08:00

Earthquake Effect Around the World

Earthquakes are caused principally by rupture of geological faults, however additionally by different events like volcanic activity, landslides, mine blasts, and nuclear tests. An earthquake's purpose of initial rupture is named its focus or hypocenter. The epicenter is that the purpose at ground level directly higher than the hypocenter. The ground shaking may also cause landslides, mudslides, and avalanches on steeper hills or mountains, all of which can damage buildings and hurt people. The second main earthquake hazard is ground displacement (ground movement) along a fault.

Earthquakes square measure measured exploitation observations from seismometers. The instant magnitude is that the most typical scale of that earthquake larger than roughly five square measures reported for the whole globe. The a lot of various earthquakes smaller than magnitude five reported by national geophysical science observatories square measure measured totally on the native magnitude scale, additionally observed because the Richter magnitude scale. These 2 scales, square measures numerically similar over their vary of validity.

Magnitude three or lower earthquakes square measure principally virtually unperceivable or weak and magnitude seven and over doubtless cause serious harm over larger areas, reckoning on their depth. The biggest earthquakes in historic times are of magnitude slightly over nine, though there's no limit to the potential magnitude. The foremost recent massive earthquake of magnitude nine. Intensity of shaking is measured on the changed ordered series. The shallower associate earthquake, the a lot of harm to the structures it causes, all else being equal.

At the surface, earthquakes manifest themselves by shaking and generally displacement of the bottom. Once the geographical point of an oversized earthquake is found offshore, the ocean bottom could also be displaced sufficiently to cause a moving ridge. Earthquakes may also trigger landslides, and sometimes volcanic activity.

Lets see some effect of this earthquake event surround the world.

Earthquake Effect Around the World

Advantages and Disadvantages of Ready Mix Concrete

2017-02-08T23:48:00.002+08:00

What is Ready Mix Concrete ?

What is Ready mix concrete ? Ready mix concrete refers to concrete that is specifically manufactured for delivery to the customer's construction site in a freshly mixed and plastic or unhardened state. Concrete itself is a mixture of Portland cement, water and aggregates comprising sand and gravel or crushed stone.

Ready-mix concrete is concrete that is manufactured in a factory or batching plant, according to a set recipe, and then delivered to a work site by truck mounted in–transit mixers. This results in a precise mixture, allowing specialty concrete mixtures to be developed and implemented on construction sites. Ready-mix concrete is often preferred over on-site concrete mixing because of the precision of the mixture and reduced work site confusion.

Advantages of Ready Mix Concrete

Ready Mix Concrete (RMC) allows speedy construction through programmed delivery at site, mechanized operation with consequent economy.
RMC reduces the labour cost and site supervising cost.
RMC comes with consistency in quality through accurate & computerized control of sand aggregates and water as per mix designs.
Production of RMC helps in minimizing cement wastage due to bulk handling.
Production of RMC is relatively pollution free.
Reduced project time resulting in savings in all aspects.
Proper control and economy in use of raw material resulting in saving of natural resources.

Disadvantages of Ready Mix Concrete

The materials are batched at a central plant, and the mixing begins at that plant, so the traveling time from the plant to the site is critical over longer distances. Some sites are just too far away, however the use of admixtures like retarder can be added.
Furthermore, access roads and site access have to be able to carry the greater weight of the ready-mix truck plus load. (Green concrete is approx. 2.5 tonne per m³.) This problem can be overcome by utilizing so-called 'mini mix' companies which use smaller 4m³ capacity mixers able to reach more-restricted sites.
Concrete's limited time span between mixing and curing means that ready-mix should be placed within 210 minutes of batching at the plant. Modern admixtures can modify that time span precisely, however, so the amount and type of admixture added to the mix is very important.

Definition of Limecrete and its Benefit

2017-02-08T00:17:00.001+08:00

Definition of Limecrete and its Benefit

Ever heard of Limecrete? Limecreteor lime concrete is concrete where cement is replaced by lime. One successful formula was developed in the mid-1800s by Dr. John E. Park. We know that lime has been used since Roman Times either as mass foundation concretes or as lightweight concretes using a variety of aggregates combined with a wide range of pozzolans (fired materials) that help to achieve increased strength and speed of set.

This meant that lime could be used in a much wider variety of applications than previously such as floors, vaults or domes. Over the last decade, there has been a renewed interest in using lime for these applications again. This is because of environmental benefits and potential health benefits, when used with other lime products.

Environmental Benefits of Limecrete

Lime is burnt at a lower temperature than cement and so has an immediate energy saving of 20% (although kilns etc. are improving so figures do change). A standard lime mortar has about 60-70% of the embodied energy of a cement mortar. It is also considered to be more environmentally friendly because of its ability, through carbonation, to re-absorb its own weight in Carbon Dioxide (compensating for that given off during burning).

Lime mortars allow other building components such as stone, wood and bricks to be reused and recycled because they can be easily cleaned of mortar/limewash. Lime enables other natural and sustainable products such as wood (including woodfibre, wood wool boards), hemp, straw etc. to be used because of its ability to control moisture.

Health Benefits of Limecrete

Lime plaster is hygroscopic (literally means 'water seeking') which draws the moisture from the internal to the external environment, this helps to regulate humidity creating a more comfortable living environment as well as helping to control condensation and mould growth which have been shown to have links to allergies and asthmas. Lime plasters and limewash are non-toxic, therefore they do not contribute to indoor air pollution unlike some modern paints.

Shotcrete Definition and its Application

2017-02-05T14:09:00.003+08:00

Shotcrete Definition and its Application

Ever heard of shotcrete ? Function of shotcrete, advantages and disadvantages of shotcrete ? Lets read ! Shotcrete is concrete (or sometimes mortar) conveyed through a hose and pneumatically projected at high velocity onto a surface, as a construction technique. It is reinforced by conventional steel rods, steel mesh, and/or fibers. Fiber reinforcement (steel or synthetic) is also used for stabilization in applications such as slopes or tunneling. The greatest advantage of the process is that shotcrete can be applied overhead or on vertical surfaces without formwork.

It is often used for concrete repairs or placement on bridges, dams, pools, and on other applications where forming is costly or material handling and installation is difficult. Shotcrete is usually an all-inclusive term for both the wet-mix and dry-mix versions. In pool construction, however, the term "shotcrete" refers to wet-mix and "gunite" to dry-mix. In this context, these terms are not interchangeable (see "Shotcrete vs. gunite" discussion below).

Shotcrete is placed and compacted at the same time, due to the force with the nozzle. It can be sprayed onto any type or shape of surface, including vertical or overhead areas. Shotcrete is frequently used against vertical soil or rock surfaces, as it eliminates the need for formwork. It is sometimes used for rock support, especially in tunneling. Shotcrete is also used for applications where seepage is an issue to limit the amount of water entering a construction site due to a high water table or other subterranean sources.

This type of concrete is often used as a quick fix for weathering for loose soil types in construction zones. There are two application methods for shotcrete which is dry mix and wet mix.

1. Dry mix
The dry mixture of cement and aggregates is filled into the machine and conveyed with compressed air through the hoses. The water needed for the hydration is added at the nozzle. The dry mix method involves placing the dry ingredients into a hopper and then conveying them pneumatically through a hose to the nozzle. The nozzleman controls the addition of water at the nozzle. The water and the dry mixture is not completely mixed, but is completed as the mixture hits the receiving surface.

This requires a skilled nozzleman, especially in the case of thick or heavily reinforced sections. Advantages of the dry mix process are that the water content can be adjusted instantaneously by the nozzleman, allowing more effective placement in overhead and vertical applications without using accelerators. The dry mix process is useful in repair applications when it is necessary to stop frequently, as the dry material is easily discharged from the hose.

2. Wet mix
The mixes are prepared with all necessary water for hydration. The mixes are pumped through the hoses. At the nozzle compressed air is added for spraying.Wet-mix shotcrete involves pumping of a previously prepared concrete, typically ready-mixed concrete, to the nozzle. Compressed air is introduced at the nozzle to impel the mixture onto the receiving surface.

The wet-process procedure generally produces less rebound, waste (when material falls to the floor), and dust compared to the dry-mix process. The greatest advantage of the wet-mix process is all the ingredients are mixed with the water and additives required, and also larger volumes can be placed in less time than the dry process. For both methods additives such as accelerators and fiber reinforcement may be used.

Definition of Bottom Ash

2017-01-29T23:20:00.003+08:00

Definition of Bottom Ash

Bottom Ash is formed when ash adheres as hot particles to the boiler walls, agglomerates and then falls to the base of the furnace at a temperature around 12000 Celsius (Kim et al., 2006). Bottom Ash is coarse, with grain sizes spanning from sand to gravel, granular, incombustible by-product, and solid mineral residue.

Depending on the boiler furnace types, the Bottom Ash collected is classified into two types: dry Bottom Ash and wet Bottom Ash (more commonly referred to as boiler slag). The incombustible mineral elements stick together until they are heavy enough causes them to be removed from the bottom of the furnaces either in a wet or dry condition and is transported to handling areas by conveyor or pipe. Bottom Ash is angular in shape and ranges in colour from a medium brown or medium grey to almost black. Bottom Ash is much coarser and more highly fused than fly ash, but has a similar chemical composition to fly ash (Lee, 2008).

Bottom ash is part of the non-combustible residue of combustion in a furnace or incinerator. In an industrial context, it usually refers to coal combustion and comprises traces of combustibles embedded in forming clinkers and sticking to hot side walls of a coal-burning furnace during its operation. The portion of the ash that escapes up the chimney or stack is, however, referred to as fly ash. The clinkers fall by themselves into the bottom hopper of a coal-burning furnace and are cooled. The above portion of the ash is referred to as bottom ash too.

Definition of High Strength Concrete

2017-01-29T11:00:00.000+08:00

Definition of High Strength Concrete

High-strength concrete has a compressive strength greater than 40 MPa (5800 psi). In the UK, BS EN 206-1 defines High strength concrete as concrete with a compressive strength class higher than C50/60. High-strength concrete is made by lowering the water-cement (W/C) ratio to 0.35 or lower. Often silica fume is added to prevent the formation of free calcium hydroxide crystals in the cement matrix, which might reduce the strength at the cement-aggregate bond.

The definition of high strength concretes is continually developing. In the 1950s a cube strength of 35 MPa was considered high strength, and in the 1960s compressive strengths of up to 50 MPa were being used commercially. More recently, compressive strengths approaching 140 MPa have been used in cast-in-place buildings.

Eurocode 2 allows for concrete strengths of up to 105 MPa cube strength. There is no definition of high strength concrete in Eurocode 2, but the measures and formula change when the concrete strength is greater than C50/60 so this seems a reasonable working definition. High-strength concrete columns can hold more weight and therefore be made slimmer than regular strength concrete columns, which allows for more usable space, especially in the lower floors of buildings.

Low W/C ratios and the use of silica fume make concrete mixes significantly less workable, which is particularly likely to be a problem in high-strength concrete applications where dense rebar cages are likely to be used. To compensate for the reduced workability, superplasticizers are commonly added to high-strength mixtures.

Aggregate must be selected carefully for high-strength mixes, as weaker aggregates may not be strong enough to resist the loads imposed on the concrete and cause failure to start in the aggregate rather than in the matrix or at a void, as normally occurs in regular concrete. In some applications of high-strength concrete the design criterion is the elastic modulus rather than the ultimate compressive strength.

Testing to Determine Compressive Strength of Concrete

2017-01-29T00:51:00.001+08:00

Testing to Determine Compressive Strength of Concrete

Engineers usually specify the required compressive strength of concrete, which is normally given as the 28-day compressive strength in megapascals (MPa) or pounds per square inch (psi). Twenty eight days is a long wait to determine if desired strengths are going to be obtained, so three-day and seven-day strengths can be useful to predict the ultimate 28-day compressive strength of the concrete.

A 25% strength gain between 7 and 28 days is often observed with 100% OPC (ordinary Portland cement) mixtures, and between 25% and 40% strength gain can be realized with the inclusion of pozzolans and supplementary cementitious materials (SCMs) such as fly ash and/or slag cement.

Strength gain depends on the type of mixture, its constituents, the use of standard curing, proper testing by certified technicians, and care of cylinders in transport. For practical immediate considerations, it is incumbent to accurately test the fundamental properties of concrete in its fresh, plastic state.

Concrete is typically sampled while being placed, with testing protocols requiring that test samples be cured under laboratory conditions (standard cured). Additional samples may be field cured (non-standard) for the purpose of early 'stripping' strengths, that is, form removal, evaluation of curing, etc. but the standard cured cylinders comprise acceptance criteria.

Concrete tests can measure the "plastic" (unhydrated) properties of concrete prior to, and during placement. As these properties affect the hardened compressive strength and durability of concrete (resistance to freeze-thaw), the properties of workability (slump/flow), temperature, density and age are monitored to ensure the production and placement of 'quality' concrete. Depending on project location, tests are performed per ASTM International, European Committee for Standardization or Canadian Standards Association.

As measurement of quality must represent the potential of concrete material delivered and placed, it is imperative that concrete technicians performing concrete tests are certified to do so according to these standards. Structural design, concrete material design and properties are often specified in accordance with national/regional design codes such as American Concrete Institute.

Compressive strength tests are conducted by certified technicians using an instrumented, hydraulic ram which has been annually calibrated with instruments traceable to the Cement and Concrete Reference Laboratory (CCRL) of the National Institute of Standards and Technology (NIST) in the U.S., or regional equivalents internationally.

Standardized form factors are 6" by 12" or 4" by 8" cylindrical samples, with some laboratories opting to utilize cubic samples. These samples are compressed to failure. Tensile strength tests are conducted either by three-point bending of a prismatic beam specimen or by compression along the sides of a standard cylindrical specimen. These destructive tests are not to be equated with nondestructive testing using a rebound hammer or probe systems which are hand-held indicators, for relative strength of the top few millimeters, of comparative concretes in the field.

Shrinkage Cracks of Concrete

2017-01-28T01:06:00.000+08:00

Shrinkage Cracks of Concrete

Shrinkage cracks occur when concrete members undergo restrained volumetric changes (shrinkage) as a result of either drying, autogenous shrinkage or thermal effects. Restraint is provided either externally (i.e. supports, walls, and other boundary conditions) or internally (differential drying shrinkage, reinforcement). Once tensile strength of the concrete is exceeded, a crack will develop.

The number and width of shrinkage cracks that develop are influenced by the amount of shrinkage that occurs, the amount of restraint present and the amount and spacing of reinforcement provided.These are minor indications and have no real structural impact on the concrete member.

Plastic-shrinkage cracks are immediately apparent, visible within 0 to 2 days of placement, while drying-shrinkage cracks develop over time. Autogenous shrinkage also occurs when the concrete is quite young and results from the volume reduction resulting from the chemical reaction of the Portland cement.

Tension Crack of Reinforced Concrete

2017-01-27T13:17:00.000+08:00

Tension Crack of Reinforced Concrete

Concrete members may be put into tension by applied loads. This is most common in concrete beams where a transversely applied load will put one surface into compression and the opposite surface into tension due to induced bending. The portion of the beam that is in tension may crack. The size and length of cracks is dependent on the magnitude of the bending moment and the design of the reinforcing in the beam at the point under consideration.

Reinforced concrete beams are designed to crack in tension rather than in compression. This is achieved by providing reinforcing steel which yields before failure of the concrete in compression occurs and allowing remediation, repair, or if necessary, evacuation of an unsafe area.

Thermal Expansion and Shrinkage of Concrete

2017-01-27T00:05:00.001+08:00

Thermal Expansion and Shrinkage of Concrete

Concrete properties has a very low coefficient of thermal expansion. However, if no provision is made for expansion, very large forces can be created, causing cracks in parts of the structure not capable of withstanding the force or the repeated cycles of expansion and contraction. The coefficient of thermal expansion of Portland cement concrete is 0.000008 to 0.000012 (per degree Celsius).

As concrete matures it continues to shrink, due to the ongoing reaction taking place in the material, although the rate of shrinkage falls relatively quickly and keeps reducing over time (for all practical purposes concrete is usually considered to not shrink due to hydration any further after 30 years). The relative shrinkage and expansion of concrete and brickwork require careful accommodation when the two forms of construction interface.

Due to its low thermal conductivity, a layer of concrete is frequently used for fireproofing of steel structures. However, the term fireproof is inappropriate, for high temperature fires can be hot enough to induce chemical changes in concrete, which in the extreme can cause considerable structural damage to the concrete.

Construction of The Burj Khalifa

2017-01-25T23:41:00.005+08:00

Construction of The Burj Khalifa

The Burj Khalifa also known as 'Khalifa Tower in Dubai' is currently the tallest structure in the world which is at 829.8 meter high (2722 ft). The construction of the 163 floor Burj Khalifa started at 6th January 2004 and completed at 2nd December 2009. It is officially open for public at 4th January 2010. The Burj Khalifa which surpassed The Taipei 101 costs around USD 1.5 billion at that time.

The mastermind behind tallest structure in the world !

The mastermind behind this project is Adrian Smith (The architect) and Bill Baker (The structural engineer). The primary structure basically is reinforced concrete. The Burj Khalifa was designed by Adrian Smith, then Skidmore, Owings & Merrill (SOM), whose firm designed the Willis Tower and One World Trade Center. Hyder Consulting was chosen to be the supervising engineer with NORR Group Consultants International Limited chosen to supervise the architecture of the project.

The tower was constructed by Samsung C&T from South Korea, who also did work on the Petronas Twin Towers and Taipei 101. Samsung C&T built the tower in a joint venture with Besix from Belgium and Arabtec from UAE. Turner is the Project Manager on the main construction contract. Over 45,000 m3 of concrete, weighing more than 110,000 tonnes were used to construct the concrete and steel foundation, which features 192 piles; each pile is 1.5 metre diameter x 43 m long, buried more than 50 m deep.

The foundation of The Burj Khalifa

The foundation is designed to support the total building weight of approximately 450,000 tonnes. This weight is then divided by the compressive strength of concrete of which is 30 MPa which yield a 450 sq.meters of vertical normal effective area which then yield to a 12 meters by 12 meters dimensions.

A high density, low permeability concrete was used in the foundations of Burj Khalifa in which the Ultimate Compressive Strength reach as much as 30 MPa, an effective area in which concrete is sandwiched by the pile, the column is 12 meters by 12 meters and the thickness as low as possible. A cathodic protection system under the mat is used to minimise any detrimental effects from corrosive chemicals in local ground water.

Records achieved by The Burj Khalifa

World highest building, huge expertise, and huge cost. For sure, the will be lots of greatest records can be achieved by The Burj Khalifa which is ;

Tallest existing structure: 829.8 m (2,722 ft)
Tallest structure ever built: 829.8 m (2,722 ft)
Tallest freestanding structure: 829.8 m (2,722 ft)
Tallest skyscraper (to top of spire): 829.8 m (2,722 ft)
Tallest skyscraper to top of antenna: 829.8 m (2,722 ft)
Building with most floors: 211 (including spire)
Building with world's highest occupied floor: 584.5 m (1,918 ft)
World's highest elevator installation.
World's longest travel distance elevators: 504 m (1,654 ft)
Highest vertical concrete pumping (for a building): 606 m (1,988 ft)
World's tallest structure that includes residential space
World's highest observation deck: 148th floor at 555 m (1,821 ft)
World's highest outdoor observation deck: 124th floor at 452 m (1,483 ft)
World's highest installation of an aluminium and glass façade: 512 m (1,680 ft)
World's highest nightclub: 144th floor
World's highest restaurant (At.mosphere): 122nd floor at 442 m (1,450 ft)
World's highest New Year display of fireworks.

Right now, your already know about the tallest structure in the world which is The Burj Khalifa, Dubai. But did you know which is tallest twin tower in the world right now? Ever heard of Petronas Twin Tower in Kuala Lumpur ?

Construction of Petronas Twin Towers KLCC

2017-01-24T21:49:00.000+08:00

Construction of Petronas Twin Towers KLCC

Petronas Twin Towers, also known as Menara Berkembar Petronas in malay language, are twin skyscrapers in Kuala Lumpur, Malaysia. They were the tallest buildings in the world from 1998 to 2004 and remain the tallest twin towers in the world. The buildings are a landmark of Kuala Lumpur, along with nearby Kuala Lumpur Tower.

The tallest building in the world from 1 January 1998 to 31 December 2004

Built on 1 January 1992 until 31 December 1994, the Petronas Twin Towers was the tallest building in the world from 1 January 1998 to 31 December 2004. Currently, it still holds the record for the tallest twin buildings in the world. It is the headquarters of Petronas, a Fortune 100 state owned oil company and also the largest company in South East Asia.

The towers and the mall below were designed by Argentinian born architect César Pelli. Construction started in 1991 and completed 7 years after, in midst of Asian Financial Crisis and Reformasi movement. Due to the soil conditions on the tower, the buildings were built on one of the deepest foundations in the world. The Building Services Engineer was Flack + Kurtz who is currently part of the WSP | Parsons Brinkerhoff Company.

The 88-storey towers were built using mostly reinforced concrete, with steel-and-glass facade to resemble Islamic motifs, a religion followed by the majority of Malaysia. The cross section of the tower resembles Rub el Hizb, further solidifies the Islamic motif in the tower design.

The construction of the superstructure commenced on 1 April 1994. Interiors with furniture were completed on 1 January 1996, the spires of Tower 1 and Tower 2 were completed on 1 March 1996, and the first batch of Petronas personnel moved into the building on 1 January 1997. The building was officially opened by the Prime Minister of Malaysia's Tun Dr. Mahathir bin Mohamad on 1 August 1999.

The twin towers were built on the site of Kuala Lumpur's race track.Test boreholes found that the original construction site effectively sat on the edge of a cliff. One half of the site was decayed limestone while the other half was soft rock. The entire site was moved 61 metres (200 ft) to allow the buildings to sit entirely on the soft rock.

Petronas Twin Towers were built on the world's deepest foundations

Because of the depth of the bedrock, the buildings were built on the world's deepest foundations. 104 concrete piles, ranging from 60 to 114 metres (197 to 374 ft) deep, were bored into the ground. The concrete raft foundation, comprising 13,200 cubic metres (470,000 cu ft) of concrete was continuously poured through a period of 54 hours for each tower.

The raft is 4.6 metres (15 ft) thick, weighs 32,500 tonnes (35,800 tons) and held the world record for the largest concrete pour until 2007. The foundations were completed within 12 months by Bachy Soletanche and required massive amounts of concrete. The Petronas Towers' structural system is a tube in tube design, invented by Fazlur Rahman Khan. Applying a tube-structure for extreme tall buildings is a common phenomenon.

The 88-floor towers are constructed largely of reinforced concrete, with a steel and glass facade designed to resemble motifs found in Islamic art, a reflection of Malaysia's Muslim religion. Another Islamic influence on the design is that the cross section of the towers is based on a Rub el Hizb, albeit with circular sectors added to meet office space requirements.

The halt in construction had cost US$700,000 per day

Early into construction a batch of concrete failed a routine strength test causing construction to come to a complete halt. All the completed floors were tested but it was found that only one had used a bad batch and it was demolished. As a result of the concrete failure, each new batch was tested before being poured. The halt in construction had cost US$700,000 per day and led to three separate concrete plants being set up on the site to ensure that if one produced a bad batch, the other two could continue to supply concrete.

The sky bridge contract was completed by Kukdong Engineering & Construction. Tower 2 became the first to reach the world's tallest building at the time. When the structure reached about 72nd floor, tower 2 ran into problems. They discovered the structure was leaning 25 millimetres (0.98 in) off from vertical. To correct the lean, the next 16 floors were slanted back 20 millimetres (0.79 in) with specialist surveyors hired to check verticality twice a day until the building's completion.

The building twice as heavy on its foundation as a comparable steel building.

Due to the huge cost of importing steel, the towers were constructed on a cheaper radical design of super high-strength reinforced concrete. High-strength concrete is a material familiar to Asian contractors and twice as effective as steel in sway reduction; however, it makes the building twice as heavy on its foundation as a comparable steel building.

Supported by 23-by-23 metre concrete cores and an outer ring of widely spaced super columns, the towers use a sophisticated structural system that accommodates its slender profile and provides 560,000 square metres of column-free office space.